Method of artificially producing carbonaceous composition pieces



Nov. 7, 1950 P. MULLER 2,529,041

METHOD 0F ARTIFICIALLY PRODUCING cARBoNAcEous couPosITIoN PIECES Filed Dec. 16, 1946 INVENTOR v *paul 6'" t Y`v 'Bli NAI s( ATTORNEYS.

Patented Nov. 7, 195'() METHOD OF ARTIFICI'LLY PRODUCING CARBONACEOUS COMPOSITION PIECES Paul Mller, Sierre, Switzerland, assignorvto Societe Anonyme pour lIndustrie de lAluminium, Chippis, Switzerland, a joint-stock company of Switzerland Application December 16', 1946, Serial No. 716,668

5 Claims. (Cl. lil-54.7)

This invention is a novel method of producing baked carbonaceous articles. Artificially produced carbonaceous composition pieces are used for various purposes, for example for electrodes Y of arc furnaces, as anodes for the electrolytic production of aluminium, vas shaped blocks for the hearths of electrometallurgical furnaces, and like uses.

The .conventional method of producing such pieces consists essentially in mixing a raw material composed substantially of carbon (for example ground coke) together with a binder (for instance coal-pitch), thereafter compressing to shape the mixture, and then baking itat a high temperature. The raw materials are thoroughly mixed and at the same time usually also kneaded. According to the composition the mixture in consistency may vary from crumbly to viscous. Generally it is brought into the desired shape by pressing, ramming or pouring when heated to a temperature between 60 and 200 C. Thereupon the baking is carried out; continuing for several hours or days at temperatures attain ing for instance 1200 C. During this treatment.v

the binder becomes coked and the amorphous carbon may be transformed gradually into graphite, if the temperatures are sufficiently high, whereby the ash contents become lowered. If the mixture is shaped by pouring, it .may be suitable to subject it to vibrations of a frequency of several thousands per minute before baking,`

them while still hot into a baking furnace. With this method it is suitable to coke the surface of the hot shaped pieces before introducing them into the baking furnace, this coking step being done by putting the pieces on glowing iron plates, after wrapping them in paper in order to avoid .a direct contact with the glowing metal.

all the carbon is transformed into graphite,

more economical.

each carbonaceous raw mass composed substan- Such a method is suitable principally for makl l ing artificial carbon pieces ofl relatively small size.l

Also, gas heated annular kilns are used for bak,- ing the shaped carbon pieces.

which the artificial carbon pieces are embedded; and metallic conductors, which serve asv heating conductors, may be disposed in the filling powder.

The present invention relatesl to a method of artificially producing carbonaceous composition pieces, this new method involving improvements including, important simplifications or compared with the known processes, and being therefore According to the invention,

change of position, preferably until `complete graphitization. In electric resistance furnaces in which the heat is produced in the interior of the carbonaceous mass or of the filling powyderor of both, it is found most suitable that with several artificial carbon pieces they form a row without intervals.

If the articial carbon pieces occupy a sufficient height in the furnace before baking, for example in the case of large electrodes, it is observable during the electric baking with heat generation in the interior, that the lower strata of the charge are-hotterl than the upper ones, because the latter are less compressed and present therefore a greater resistancerto the electric current than the lowered strata, and because the heat losses are greater at the top, if the furnace is not provided with a well heat-insulated cover. Therefore each mass is baked gradually from vthe bottom to the top and a setting of the mass takes place during the baking; Vthis setting bee ing very advantageous because it increases theA density of the baked pieces. If the height of the artificial carbon pieces is suiciently low, this phenomenon does not take place as the temperature differences are vertically too small. With gas heated furnaces the heat is not produced in the interior of the carbonaceous mass or of the filling powder but is supplied from the exterior, so that the advantageous setting can'- not take place; on the contrary, the baking proseeds at all sides from the' exterior to 'the in! But electric resistance furnaces may also beused, which, like 'the lgas heated ones, -contain a filling powder in 3 terior and in some cases blow-holes are formed or inner tensions occur which lead to the bursting or rupturing of the pieces. According therefore to a further improvement of the invention the baking is carried out in electric resistance furnaces, and the height ofthe artificial carbon pieces inthe furnace is chosen in such a manner that substantial temperature differences occur between the lowerl and the upper parts of the pieces and that the baking proceeds gradually from the bottom to the top. l It is possible to prepare and sary mold spaces for the reception ofthe carbonaceous mass; in this case theffilling powder answers the same purpose as the sand used in the casting of metals in sand molds.

A very practical and advantageous mode of operation with this invention consists in placing on the furnace sole, which has been covered with a layer of filling powder, sheet-metal boxeswhich have no bottom nor top walls and are therefore provided only with side walls, and lling the 'inl ters'paces between boxes vand walls vwith filling powder. The :carbonaceous mixtureisA then pouredinto the sheet-metal boxes, the boxes are drawn away vertically and the whole assemblyisV covered? with a-layer of `filling powder. The sheetme'tal'boxes are immediately ready for reuse. In order-to avoid the artificial carbon pieces sticking together and to the filling' powder the boxesv may be lined with paper or wrapped in paper lbefore Vpouring the carbonaceous mass. When the boxes are drawn awa-y'upwardly'as above Stated'being madebottomless for this purpose, the paper remains behind and forms a separating layer which is coked during the following baking, and thus prevents a sticking of the artificial carbon pieces, and moreover leaves on their surface a hard layer, with the effect that the filling powder can be very easily detached from the baked carbon pieces. The sheet-metal boxes are suitably' made from sheet-iron,'but can ofcourse be made. also ,from another .-r'netal. Each of the fopen-bottom boxes or molds is lifted outof the furnace after the pouring but before -the bakingof-the mass, asA

.alread'yrecited' to secure the advantages and results of the invention. This leaves nom'etal `subject tofmelting, possiblyv toimpair the product; this advantage prevailing even lif the'bakin'g is continued until complete graphitization. The molds are salvaged unimpaired and ready for immediate reuse, reducing the operations. Also' the 'costs are minimized both as to supplying many molds and storing them.' i These process factorsV 'may be `summed upas charging the raw mass into the vsheet-metal bottomless molds or boxes as the latter rest` upon the filling layer which covers the furnace sole, with filling powder also vsurrounding the molds; and thereupon drawing away vertically the molds, and then completing the filldispose they iill- Y ing powder so that it is provided with the necesas a heating conductor. powder answers three different purposes, namely:

baking electrodes. In these cases boxes made from thin wood or from cardboard can be used instead of sheet-metal boxes. Ihe baking `can be carried out in gas fired annular kilns, But the electric resistance furnaces are the most suitable; in these furnaces the carbonaceous mass to be baked provides'the resistance. As the carbonace- Aous mass freshly lled in has only a very low electric conductivity at the beginning, heat may be produced in special heating conductors at the beginningof the baking. For this purpose it is suitable to use the lling powder at least partly In this case the filling it maintains the artificial carbon pieces in the desired shape, it absorbs the volatile constituents which escape f romk the carbonaceous mass and it conducts the electric current. For this purpose f vthe lling powder consists advantageously of coke such as is used in a known type of electric resistance furnace. Besides coke there can be used as lling` powder for instancamixtures of ground coke' with. bauxite powder, graphite, anthracite' or alumina. After the burning the filling powder sticks generally together and must be broken.

The detaching from the artificial carbon is very .The `method and principles hereinabove disclose'd may be carried outin different forms of furace,"of which that shown in the drawings is aY typical example. The furnace may be forexample-L meters wide and l.'7 meters high, and of extended length toepermit charging the furnace with an extended row. or series-of molds so that a single baking can turn out a considerable number of products. Fig. Y1 isa side elevation of an electrical resistancefurnace suitable for the purpose; with its middle portion shown in longitudinal vertical section to disclose the characteristic molds and other elements; the furnace being in the process of being charged with a row ofV poured and molded articles, to be simultaneously baked into a number of products. Fig. 2', in

'- top plan view on a larger scale than Fig. .1, is a briquette forms andto'introduce the solidified briquettes into the furnace after heating them again, or., without reheating, asis. done with.y self:-

horizontal section on the line 2--2 of Fig. l. Fig. 3 is a perspective view of one of a series of the individual metal molds, containing sheets of lining material, such as paper, to serve as separators or septum's between, and thus constitute wrappings for, a row of the articles to be baked. Fig. 4`

is a side elevation 'of a modified arrangement wherein the septums or paper separators are placed outside the metal molds and 'thus constitute Wrappings for the molds.

In the selected lillustration the furnace is bounded by its sideand end walls 5, composed of refractory material such as firebricks, and at the bottom a similar wall Sconstituting the sole of the furnace', no rigid cover being necessary. Metallic frame parts may be embodied in the furna'ce,.ie..,g..str'aps.1, as of. steel, which may surround and bind the refractory walls a't the sides and ends.

The generation of heat is on the electrical resistance principle; for which there is shown an electrical terminal member Brat each end operating to carry the power into the furnace interior, to operate upon the charged contents of the furnace, the molded masses and filling powder, to develop the necessary high baking temperatures. For each lead-in terminal 8 there is shown an exterior conductor or cable 9 energized from a convenient power source at appropriate potential and current.

For the purpose of isolating and supporting the articles to be produced these are, during the baking period, surrounded'by a ller or powder II consisting preferably of a body of ground coke, which thereby acts like a sand or similar mold, confining and maintaining the shape of the masses until baked. Thus, rst, within the bot` tom of the furnace, is a layer I I of the fillingv powder, overlying the sole to a substantial depth and serving-initially as a support for the metal molds and shaped products within the furnace. This layerIl appears in Fig. l also in Fig. 2, while Fig. 2 shows similarr upright deposits or layers I2, inserted progressively between the introduced molds and the side and end walls of the furnace; so that, when fully charged, the complete row of articles, ready for the baking step, is surrounded and enclosed at bottom and sides. By way of completing the enclosing of the mold series and products there is preferably added a top layer I3, overlying the articles to a f substantial depth as seen in Fig. 1,

The lengthwise row 'of products I5, whether electrodes for arc furnaces or other articles to be more or less graphitized, may extend substantially from end to end; the rst molded mass I5a being shown at the left in Fig. 2, the adjacent gap indicating one or more larticles |51), IEC, the latter showing in Fig. 1, followed by product ld seen in Figs. 1 and 2. Down to this point in the charging operation the molds have been extracted, relying upon interposed septums to maintain separation between products. Product I5e has been completely cast, but its mold not yet lifted out, while the next product If is shown being poured, into the next mold Zf. Other spaces beyond are yet to be provided with molds 20g etc. and poured to complete the charging of the furnace.

In Fig. 1 the molten and owable carbonaceous mass is shown being poured from a supply mass vI6 contained in a ladle I'I, which is tiltably supported, as by rods I3, and can be shifted along from mold to mold, during charging, in the direction of the arrow.

Of the molds 20, three or four'may suiiice for charging a long furnace, having capacity for six or more molds, namely, by reason of each mold upon extraction being advanced to and applied at a new position The molds may be like boxes, of sheet iron, of various sectional shapes, as round, but square being shown. The sides of each mold are closed but the top and bottom are open. When set in, each mold rests on the previously laid filler layer II over the sole 6.

The oldest mold that appears in Figs. 1 and 2 is mold 25e, containing product I5e, theprevious molds having been withdrawn. After the initial or partial setting of the mass I5e its mold will be lifted out, away from the mass. The mold 2li is seen having the mass for the next product 20f poured into it. An empty mold 2i]g has been placed, ready for the next pouring thereafter, from the advanced ladle. Y As the setting down into place of the molds proceeds, the filling powder I2k may be placed between the mold row and the end and side walls, with compacting if desired; and as the removal of molds progresses the supplying of iilling powder for the top layer I3 may be carried along, so that finally the row of products, about to be backed, becomes wholly embedded in and isolated by the ller material, which serves also as a resistance heat source, and a conductor adapted to. transmit heat to the articles to be baked. By allowing an appreciable space between each two molds, these spaces, upon the extraction of the molds may be lled or stuffed with filler before baking, affording more complete heat penetration. Lifting eyes or handles ZI on the molds, Fig. 3, help in depositing and withdrawing them. Y

I t is of important advantage to provide, for each moldv and product, a septum or separating liner 22 of thin sheet material, preferably paper, arranged in tight sheet contact within the mold. As shown, the liner or other septum 22 may be slightly less tall than the mold, reachingV almost to the top, and providing a guide in the pouring of the warm pasty material intothe mold, las well seen in Fig. l; the additional height of the mold assisting in its extraction, aided by the eyes 2|. The paper septum prevents both the sticking of the poured article to the mold and the sticking of adjoining articles to each other.` The paper during baking may become coked or incinerated under the high temperature, but nevertheless retains its function of maintaining separate the baked products.

A lining or interior septum 22 is generally satisfactory, but in some instances a wrapping septum has advantages, and Fig. fi showssuch, the septum 23 surrounding the metal mold 2Q. Ihe mold, when lifted out between the poured mass and the exterior seutum, leaves the mass wholly. separatedrfrom the next adjacent masses, preventing sticking.

The progress of the charging of the furnace, from the viewpoint of each rigid mold 20 and the article Vformed therein, may bedescribed beginning with the empty mold 20g, provided with its septum in the form of wrapper or liner. Next, the mass for each mold is poured and the mold substantially lled in the manner shown at the mold 2llf, the product I5f being built up to the desired shape. When filled, and until initial hardening, the condition is shown by the mold 20e containing the product 15e. Then the mold is lifted out, leaving the products each sur-v rounded by its septum or liner, asshown by the products I5d, ISC, I5b and I5a. When the entire row or series of products has thus been molded and the molds removed, further filling powder may be placed within all of the furnace spaces not theretofore filled and up to the level of the tops of the side and end walls, as shown in Fig. 1, the top layer I3 serving as a cover, no other cover to the furnace being necessary. When all of these charging steps are attended to the furnace is ready for the baking operation. A conventional switch, not shown, is thrown to apply the current through the cables 9 and terminals 8 to and through the filling powder layers and the embedded products; whereupon the necessary interior temperatures are progressively developed and transmitted to the products, the process requiring no further attention other than awaiting the necessary baking interval.

:magenVv `ceous articles, such as electrodes for metallurgical furnaces, carried out'withthe aid of molds open at topf and bottom inan electric-resistance baking furnace in which heat is generated by electric current passing through an interior body of carbonaceous filling powder which is of high-y resistance conductivity; said method comprising placing a bottom layer of the filling powder on the sole of such a furnace, and, for each article i to be produced, setting upright such a mold upon supported below and iaterauy by the niing powder, and also leaving the separating sheet in position between the formed articles; applying over-.the molded articles an enclosing protective' warm to become pasty and take the required i form in the mold; then extracting upwardly the -retaining the formed and embedded article in its unchanged molding position in the furnace, subjecting it to an elevated baking temperature atleast until the hardening or" the article by passing an electric current through the filling powder withinY the furnace, such current passing progressively also through the hot carbonaceous article itself in the course of the baking.

2. The method as recited in claim 1 and wherein the carbonaceous mass to be baked is composed of a finely ground coke mixed with a coaltar pitch; and wherein the mass is prewarmed and charged by pouring in pasty con-A dition into the mold.

3. Themethod as recited in claim 1 and wherein the carbonaceous mass is in the form of small solid briquettes adapted to be charged as such and to become warmed, softened and molded by the starting of the baking stage.

4. The method of' producing baked carbonav paper-like materialv by placing it to serve as aY separator between articles during baking; filling theinterspaces between each mold and the furnace 'lateral walls with the filling powder;

chargingl a carbonaceous mass,- composed stantially of a finely divided carbon material premixed with a binder material, directly into each box mold to take the'required' form of 'theA article; extracting upwardly each mold while leaving each unbake'd. molded mass or article top covering of high-resistance filler within the furnace; and then, while retaining the formed and embedded articles in their unchanging molding positions in the furnace, subjecting them simultaneously to an elevated-temperature baking operation at least until the hardening yof the article by passing an electric' current through the filling powder within the furnace, during which baking operation the paperlike septum sheet functions to protect each article fromv adhering to lling powder and to adjacent articles, both before and after the disintegration by coking of the septum. y

5. In the art of molding a carbonaceous mass 1 to the form of a desired product or article and baking it to hardness in anv electric furnace, with the aid of a loose mold open attop and bottom, and wherein the mass is a premixture of a finelyv divided carbon material and a binder material and is adapted under heat to soften to mcldable consistency but with prolonged subjection to high temperature to become baked to permanent hardness; tlie method ofV charging such furnaceconsisting in,v rst, laying uponA the furnace sole a substantial bottom layer of a suitable filling powder possessing high-resistance conductivity; then introducing into the furnace a loose mold for each article to be formed and positioningA it to stand upright Vto rest removably upon such bottom layer;V adding filling powder to lill the interspaces between the loose molds and the' furnace walls, and at the same stage warming the mass to pasty consistency and charging it into each such loose mold to take' the desired form of the article; extracting bodily upwardly each such mold leaving the molded mass supported underneath and laterally by the filling powder acting as an enclosing mold, and then placing in the furnace further filling powder including a sub-v stantial top layer covering and completing the embedding of the formed article in readiness for the application of electric power to generate baking hea-t in the filling powder and molded masses.

v Y vPAUL. MULLER.

nnrEnrlN'cEs' orrED The following references are of record in the fle of this patent:

UNITED STATES PATENTS Richon July 2,', 1946 

1. THE METHOD OF PRODUCING BAKED CARBONACEOUS ARTICLES, SUCH AS ELECTRODES FOR METALLURGICAL FURNACES, CARRIED OUT WITH THE AID OF MOLDS OPEN AT TOP AND BOTTOM IN AN ELECTRIC-RESISTANCE BAKING FURNANCE IN WHICH HEAT IS GENERATED BY ELECTRIC CURRENT PASSING THROUGH AN INTERIOR BODY OF CARBONACEOUS FILLING POWDER WHICH IS OF HIGHRESISTANCE CONDUCTIVITY; SAID METHOD COMPRISING PLACING A BOTTOM LAYER OF THE FILLING POWDER ON THE SOLE OF SUCH A FURNACE, AND, FOR EACH ARTICLE TO BE PRODUCED, SETTING UPRIGHT SUCH A MOLD UPON SUCH BOTTOM LAYER; THEN FILLING THE INTERSPACES BETWEEN EACH MOLD AND THE FURANCE LATERAL WALLS WITH THE FILLING POWDER; THEN CHARGING INTO THE MOLD A RAW CARBONACEOUS MASS, COMPOSED SUBSTANTIALLY OF A FINELY DIVIDED CARBON MATERIAL PREMIXED WITH A BINDER MATERIAL ADAPTED WHEN WARM TO BECOME PASTY AND TAKE THE REQUIRED FORM IN THE MOLD; THEN EXTRACTING UPWARDLY THE MOLD LEAVING THE UNBAKED MOLDED MASS OR ARTICLE SUPPORTED BELOW AND LATERALLY BY THE FILLING POWDER, THEN COMPLETING THE SURROUNDING OF THE MOLDED ARTICLE BY APPLYING UPON THE ARTICLE AN ENCLOSING PROTECTIVE TOP COVERING, AND THEN, WHILE RETAINING THE FORMED AND EMBEDDED ARTICLE IN ITS UNCHANGED MOLDING POSITION IN THE FURNANCE, SUBJECTING IT TO AN ELEVATED BAKING TEMPERATURE AT LEAST UNTIL THE HARDENING OF THE ARTICLE BY PASSING AN ELECTRIC CURRENT THROUGH THE FILLING POWDER WITHIN THE FURNANCE, SUCH CURRENT PASSING PROGRESSIVELY ALSO THROUGH THE HOT CARBONACEOUS ARTICLE ITSELF IN THE COURSE OF THE BAKING. 